Hot springs exist in many areas in our planet. The hot springs transfer heat from deep inside earth (this heat comes from nuclear radiation) to the surface in a form that can be used.

The hot water reaches the surfaces either as hot water (thermal energy) or as steam. (kinetic energy).

There are areas with hot springs where the heat source is above 150°C, known as areas of high temperature. These areas are usually in places where active volcanoes exist. Such areas are few. Even fewer are the areas where the water is hot enough and in sufficient quantity that can be used to produce electricity.

A well known area that utilizes hot water for various purposes is Iceland.

In high temperature geothermal areas the water reaches the surface in the form of steam under pressure. Speaking in terms of energy, the nuclear radiation is converted to heat, which means that the kinetic energy of the molecules of the water increased and finally the water, is converted to steam.

The steam (water) contains dissolved salts and various solids. These salts should be removed. Therefore the steam passes first through a separation system where the salts are removed. This process does not remove all the salt from the water. For this reason the steam cannot be used directly to turn the turbines. The steam is led in the primary circuit which is a type of heat exchanger (heat transfer from one system to another system). The role of the primary circuit is to heat the water circulating in the secondary circuit. Water from the primary circuit and the water from the secondary circuit do not come into contact (think of how the radiator heats the air of the room without water leaking into the room). Water from the secondary circuit does not contain any salt. The purpose of the secondary circuit is to convert water into steam under pressure that will turn the turbines which will turn the generators that produce electricity. So the kinetic energy of water is transmitted to the turbine and there is converted into electricity.

The turbines in geothermal plants are similar to those used in thermal plants, and turbines used in nuclear plants are greater than any other turbines. The amount of steam circulating into the primary and secondary circuit is controlled and if the pressure exceeds a certain value steam is released from escape routes. This explains why in areas with geothermal plants a lot of steam coming out can be observed.

In areas of high temperature for more efficient use the steam is first used to turn a generator and then the hot water is driven to homes (and other facilities such as swimming pools) to be used for central heating and providing hot water.